The present disclosure is directed to a system and method for controlling the operation of an engine. More particularly, the present disclosure is directed to a system and method for de-rating an engine.
The operation of an internal combustion engine, such as, for example, a diesel, gasoline, or natural gas engine, may cause the generation of undesirable emissions. These emissions, which may include particulates and nitrous oxide (NOx), are generated when fuel is combusted in a combustion chamber of the engine. An exhaust stroke of an engine piston forces exhaust gas, which may include these emissions, from the engine. If no emission reduction measures are in place, these undesirable emissions will eventually be exhausted to the environment.
Research is currently being directed towards decreasing the amount of undesirable emissions that are exhausted to the environment during the operation of an engine. It is expected that improved engine design and improved control over engine operation may lead to a reduction in the generation of undesirable emissions. Many different approaches, such as, for example, engine gas recirculation and aftertreatments, have been found to reduce the amount of emissions generated during the operation of an engine. Unfortunately, the implementation of these emission reduction approaches typically results in a decrease in the overall efficiency of the engine.
Additional efforts are being focused on improving engine efficiency to compensate for the efficiency loss due to the emission reduction systems. One such approach to improving the engine efficiency involves adjusting the actuation timing of the engine valves. For example, the actuation timing of the intake and exhaust valves may be modified to implement a variation on the typical diesel or Otto cycle known as the Miller cycle. In a xe2x80x9clate intake valve closingxe2x80x9d type Miller cycle, the intake valves of the engine are held open during a portion of the compression stroke of the piston.
However, a late intake valve closing Miller cycle may be undesirable under certain operating conditions. For example, a diesel engine operating on a late intake valve closing Miller cycle will be difficult to start when the engine is cold. This difficulty arises because diesel fuel combustion is achieved when an air and fuel mixture is compressed to a certain pressure and temperature. Implementation of the late intake valve closing Miller cycle reduces the amount of air and the amount of compression within each combustion chamber. The reduced compression combined with the reduced temperature of the engine results in a lower maximum pressure and temperature of the air and fuel mixture. Thus, achieving combustion in a cold engine operating on a late intake valve closing Miller cycle may prove difficult.
In addition, during cold operation, hydraulic motors may hold the intake valves open beyond the time of normal closing as compared to during warm operation. During cold engine operating conditions, the viscosity of the oil is greater than desirable, resulting in inadequate fluid flow and inconsistent intake valve actuator operation. Thus, intake valves may not be actuated in normal operation during cold engine conditions. However, because highly pressurized air may be supplied to the cylinder, normal operation may increase the pressure level within cylinder above desirable level. As a result, damage may occur to the engine, for example, the cylinder, turbochargers, etc.
The method and system for controlling engine operation disclosed herein solves one or more of the problems set forth above.
In one aspect, the present disclosure is directed to a system for operating an internal combustion engine that includes an intake valve moveable between a first position at which fluid is blocked from flowing to or from the cylinder and a second position at which fluid is allowed to pass to or from the cylinder. The system includes a fluid actuator selectively operable to hold the intake valve from moving to the first position during a portion of a compression stroke of the engine, a source of fluid in communication with the fluid actuator, and a control valve configured to control a flow of fluid between the source of fluid and the fluid actuator. A fuel supply system is configured to supply a predetermined amount of fuel to the cylinder at an appropriate time during an engine cycle based on at least one operating parameter of the engine, and a controller is configured to determine a need to de-rate the engine based on a sensed parameter relating to viscosity of fluid from the source during an engine cycle in which the fluid actuator is not operated.
In another aspect, the present disclosure is directed to a method for controlling operation of an engine having a piston moveable in a cylinder of the engine. The method includes moving an intake valve between a first position at which fluid is blocked from flowing to or from the cylinder and a second position at which fluid is allowed to pass to or from the cylinder during an intake stroke of the piston, and selectively operating a control valve to hold the intake valve from moving to the first position during at least a portion of the compression stroke of the piston. The method further includes sensing at least one operating parameter of the engine relating to viscosity of a fluid supplied to the control valve and determining a need to de-rate the engine based on the sensed parameter relating to viscosity and the selective operation of the control valve.
In still another aspect, the present disclosure is directed to an engine including a block defining at least one cylinder and a cylinder head having at least one intake passageway leading to the at least one cylinder. The engine includes at least one intake valve moveable between a first position at which fluid is blocked from flowing to or from the cylinder and a second position at which fluid is allowed to pass to or from the cylinder, a fluid actuator configured to selectively hold the intake valve from moving to the first position during at least a portion of a compression stroke of the engine, and a source of fluid in fluid communication with the fluid actuator. The engine also includes a control valve disposed between the source of fluid and the fluid actuator and moveable between a first position to block a flow of fluid between the source of fluid and the fluid actuator and second position to allow the flow of fluid from the source of fluid to the fluid actuator. The engine further includes a fuel supply system configured to supply a predetermined amount of fuel to the cylinder at an appropriate time during an engine cycle based on at least one operating parameter of the engine. A controller may be electrically coupled to the control valve and the fuel supply system, and the controller may be configured to actuate the control valve and to reduce the amount of fuel based on the sensed parameter during an engine cycle in which the fluid actuator is not operated.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention.